The patents referenced above describe mechanisms and apparatus suitable for analyzing speciments for specific microorganisms utilizing a plastic tray or card which contains a plurality of dried culture media specific to a single genus or species of organism. The dried media are contained in separate cells in the card which are connected by a network of passageways to a filling port. When a fluid sample is inserted into the card, mixed with media in the cells, and incubated, the organisms present in the specimen interact with the specific culture media. The interaction of the specimen and the specific culture media produces characteristic optical changes in the contents of the cell which are read to indicate presence of the organisms. The optical change in each cell involves a change in light transmitting properties thereof either through a color change or a change in turbidity. The optical change usually is caused by the metabolic activity of the organism which, for example, may produce an acid which changes the color of a pH sensitive indicator in the media. The change in the light transmitting properties of the medium also can be caused by a precipitate forming in the medium due to metabolic activity of the organism or by the mass of growing colonies of the organism. The metabolically caused changes generally yield considerably earlier results than do growth caused changes. The specific media designed for use in the cards of the aforesaid system all are designed to favor growth of one genus or species of microorganism and to inhibit growth of other organisms. The media are capable of being dried and they are formulated to function in the low oxygen environment of the card described in detail in the above referenced patents.
There are several media commercially available for the isolation of streptococci. These media support the growth of all streptococci, including the group D enterococci and other non-.beta.-hemolytic streptococci.
Currently, the medium of choice for the detection of .beta.-hemolytic streptococci is blood agar. This medium supports the growth of most bacteria but, because of the incorporation of blood cells, the .beta.-streptococci cause large zones of hemolysis to aid in their detection. Another medium in common use is Streptosel Broth (BBL) which is a selective broth for streptococci. Group D. Enterococci grow well on this medium as well as some strains of staphylococci. Pikes medium and Columbia Broth are commonly used also, but for separation of streptococci in these media, blood cells must be incorporated.
It is accordingly an object of the present invention to provide a novel .beta.-streptococcus selective medium for the growth and detection of .beta.-hemolytic streptococci only, without allowing the growth of enterococci and the other non-.beta.-hemolytic streptococci, in a relatively short period.
Another object of the invention is the provision of a selective medium of the above type without requiring the incorporation of blood cells.
A still further object is to provide a selective medium of the above type which does not permit the growth of non-.beta.-hemolytic streptococci whether present individually or in combination with .beta.-hemolytic streptococci.